The present invention relates to an exposure apparatus and a device manufacturing method.
A conventional projection exposure apparatus projects a circuit pattern of a reticle (mask) onto a wafer via a projection optical system in manufacturing semiconductor devices using the photolithography technology.
Along with a demand for fine processing to a semiconductor device, a recently proposed exposure apparatus can expose a pattern as small as half an exposure wavelength. A shorter wavelength of the exposure light and a higher numerical aperture (“NA”) of the projection optical system are used for such a high resolution. An increase of a NA of the projection optical system means an increase of an angle between a perpendicular from an image plane and a traveling direction of the incident light, and is referred to as high NA imaging.
A polarization of the exposure light is crucial to high NA imaging. For example, in exposing a so-called line and space (“L & S”) pattern that has a repetition of a line and a space, the L & S pattern is formed by plane-wave two-beam interference. An incident plane is defined as a plane that contains incident direction vectors of two beams. S-polarized light is polarized light having an electric field vector perpendicular to the incident plane, and p-polarized light is polarized light having an electric field vector parallel to the incident plane. When an angle between incident direction vectors of two beams is 90°, the s-polarized beams interfere with each other and form a light intensity distribution corresponding to the L & S pattern on the image plane. On the other hand, the p-polarized beams do not interfere with each other because their electric vectors are orthogonal (or cancel out the interference effect), and the light intensity distribution becomes constant. As a consequence, no light intensity distribution corresponding to the L & S pattern is formed on the image plane. The contrast of the light intensity distribution for a mixture of the s-polarized light and the p-polarized light becomes worse on the image plane than that with only s-polarized light. As the p-polarized light ratio increases, the contrast of the light intensity distribution on the image plane lowers and finally provides no pattern.
Hence, control over the polarization state of the exposure light is necessary. For example, one proposed exposure apparatus realizes a tangential illumination by controlling the polarization state of the exposure light with a half waveplate. See Japanese Patent Application, Publication No. 2005-166871. Another proposed exposure apparatus measures the polarization state of the exposure light in the illumination optical system, and feeds the measurement result back or forward to the light source or the exposure apparatus. See Japanese Patent Applications, Publication Nos. 2005-268489 and 2003-329516. The polarization-controlled exposure light can form a light intensity distribution having a sufficient contrast on the image plane, and can expose finer patterns.
The polarization illumination in the exposure apparatus needs the light that illuminates the reticle to have a desired polarization state, or the light that forms an image on the substrate to have a desired polarization state. In addition, control over a polarization state of the exposure light at a pupil position in the illumination optical system is not always maintained on the image plane due to the influence of the optical system after the pupil position in the illumination optical system and the projection optical system. For example, due to the birefringence of a glass material and a polarization characteristic of a mirror in the illumination and projection optical systems, a polarization state changes partially (in each area of the polarization illumination) or varies with time.
However, prior art propose general control over the polarization state of the polarization illumination, and is silent about independent (or individual) controls over respective areas in the polarization illumination. Therefore, the prior art cannot handle changes of the polarization state in each area of the polarization illumination, or cannot maintain the desired polarization state. In addition, the exposure apparatus disclosed in Japanese Patent Application, Publication No. 2005-166871 particularly needs a detachment of a polarization controller from the exposure apparatus, when the polarization state varies with time, so as to adjust the polarization controller to the desired polarization state, lowering the throughput.